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Old 01-08-2011, 01:53 PM   #31
bmwrench
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Quote:
Originally Posted by s.c.m. View Post


"Bohrung" means "bore", so the displacement calculates
(7cm)²* Pi/4 * 6.4cm * 2 = 246.3 cm³ * 2 = 492,6 cm³


Best regards
Sven
I didn't expect this to turn into a math thread! The formula I've always used is PI X R Squared X Stroke, or 3.14 X 3.5 X 3.5 X 6.4 X 6.4 X The number of cylinders. Different formulas, same (almost) result: 492.352cc.
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Old 01-08-2011, 06:31 PM   #32
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Math forum, stat!

Quote:
Originally Posted by s.c.m. View Post


"Bohrung" means "bore", so the displacement calculates
(7cm)²* Pi/4 * 6.4cm * 2 = 246.3 cm³ * 2 = 492,6 cm³


Best regards
Sven
You are correct! Translation error on my part, I mixed up the bore and stroke. Nice, slightly oversquare. That has to be part of the reason for
the custom cranks. I have absolutely no doubt that it will pull 10,000rpm.

I am deeply envious of that combustion chamber shape.

I want one. This is bad. I have a basket case R50 that I have been making plans for.
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Old 01-08-2011, 06:46 PM   #33
bmwrench
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It is tempting stuff, but I wonder how the crank and case will hold up. That's a serious increase in power and RPM and those cases are getting very old. OTOH, maybe new cases will appear if problems develop. Any one who'd go to lengths they have probably won't give up easily.
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Old 01-08-2011, 06:51 PM   #34
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Quote:
Originally Posted by ericrat View Post
You are correct! Translation error on my part, I mixed up the bore and stroke. Nice, slightly oversquare. That has to be part of the reason for
the custom cranks. I have absolutely no doubt that it will pull 10,000rpm.

I am deeply envious of that combustion chamber shape.

I want one. This is bad. I have a basket case R50 that I have been making plans for.
You can figure a conservative cost of over $5K USD for a clone of that engine. Then add in the cost of a rolling chassis worthy of having that engine mated to it. I base the engine cost on what NOS, new factory BMW or new reproduction parts would cost to build an R50/2 engine.

The rod length on Dieter's engine is 135mm.

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Old 01-08-2011, 06:59 PM   #35
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Quote:
Originally Posted by bmwrench View Post
It is tempting stuff, but I wonder how the crank and case will hold up. That's a serious increase in power and RPM and those cases are getting very old. OTOH, maybe new cases will appear if problems develop. Any one who'd go to lengths they have probably won't give up easily.
A late 60's case will handle it no problem. I consider those the best iteration of the 1955-69 BMW twins case castings. Ther are many stashes of cases 'out' there to choose from for such projects.

http://www.flyingtpot.com/engine%20cases.JPG

Dieter definitely looked at the 'big picture' when building that engine. A properly designed and manufactured built up crank will handle the increased RPM. The engine uses the stock spur gear oil pump lubricaton system, which is adequate for built up crank designs. Oil flow to those rockers might be of concern for long term use, yet it is a track bike.

Carl
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Old 01-08-2011, 07:14 PM   #36
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Old 01-08-2011, 08:00 PM   #37
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Quote:
Originally Posted by Carl View Post
Vierified by the builder:
  • ~500cc engine
  • The builder did the machining himself in-house
  • The pistons are Suzuki 750 GXR Bj.91
  • Engine will spin to 10000/min
I like his design approach.

Carl
I noticed the Suzuki logo on some parts bags in one of the pictures with the head disassembled.


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Old 01-09-2011, 01:02 AM   #38
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Quote:
Originally Posted by bmwrench View Post
The formula I've always used is ...
... perfectly correct of course!
I just tried to give an answer to this "why 450cc?" question.

Best regards
Sven
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Old 01-09-2011, 02:49 PM   #39
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[QUOTE Oil flow to those rockers might be of concern for long term use, yet it is a track bike.Carl[/QUOTE]


Did I miss something?
Did he add external oil lines to the engine up to the heads?
The pre 70 bikes had no oil to the rockers other than the splash from the oil inside the pushrod tubes. If I remember correctly.
This is why you were supposed to fill up the rocker cups at every valve adjustment.
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Old 01-09-2011, 04:56 PM   #40
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Well, Dieter didn't have any dyno specs available for the R50S. His thoughts have it putting out around 50hp. I think that is reasonable and feasible for what has been done to this engine. I saw a pic of it w/ its race fairing and it looks stunning in action on the track.

He's well into his next project and it should also turn out to be as interesting as the R50S.

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Old 01-09-2011, 06:45 PM   #41
ericrat
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Quote:
Originally Posted by Carl View Post
You can figure a conservative cost of over $5K USD for a clone of that engine. Then add in the cost of a rolling chassis worthy of having that engine mated to it. I base the engine cost on what NOS, new factory BMW or new reproduction parts would cost to build an R50/2 engine.
Carl
If there is a reputable builder willing to build that for $5k, please send me a PM. I will supply the base engine.
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Old 01-09-2011, 07:03 PM   #42
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Originally Posted by ericrat View Post
If there is a reputable builder willing to build that for $5k, please send me a PM. I will supply the base engine.
ericrat,
  1. Read the post, the word 'over' is used.
  2. That build was basic for Dieter compared to his other projects. The design concept was knocked out the first time around for the R50S project. The second time around will be much less in cost.
  3. The basics that could be supplied for such a build would be a bare block, front engine cover, flywheel and a dipstick. The rest of that engine is all custom.

So, at $5K USD you're ready to step up to the plate? What's your spending range for an engine like what is in the R50S.

Carl
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